1. Field of the Invention
The invention concerns an electronic circuit for connecting a receiver to a direct current power supply with the receiver protected against connection of the current supply with reversed polarity. A circuit of this kind includes at least one higher potential line and one lower potential line.
2. Description of the Prior Art
There are various methods of protecting against polarity reversal.
A first method consists in disposing a diode in one or both of the higher and lower potential lines so that the diode allows current to flow if the connection is correct but prevents the current from flowing otherwise. This has the drawback of power dissipation in the order of 0.3 to 0.6 times the current flowing; also, the connection is broken in the event of a fault. To avoid this latter drawback it is possible to use a plurality of diodes in parallel (the power dissipation is then increased commensurately, however) and in series (diode square).
A second method consists in disposing a diode in series with a resistor between the potential lines so that the lines are short-circuited if the polarity is reversed. However, this does not totally eliminate the application of reverse polarity to the receiver; there also remains the possibility of destruction by short-circuiting of the unit to be protected (fire hazard) and the supply.
A third method consists in disposing a diode in series with a coil between the potential lines; the diode is forward biased (so that it allows the current to flow when the power supply is connected with the correct polarity) and the coil is part of a relay of which the mobile part (armature) constitutes, on one or both potential lines and on the downstream side of the diode+ coil branch, a normally open switch which closes only upon flow of current in the coil in the direction allowed by the diode, i.e. when the supply is connected correctly. This provides better protection of the receiver than the second method, but has the same drawbacks as the first solution (total loss of the connection function in the event of a fault and high power dissipation, limited only by the resistance of the relay coil).
A fourth type of method uses electromechanical devices, extensively described in the literature, but having the disadvantages of being heavy, bulky, constructed from large mechanical parts and having large airgaps.
Examples of patents in this field are:
U.S. Pat. No. 2,887,626, 19 May 1959: "Reverse Current Relay", PA1 French Patent 819 610, 19 Dec. 1960: "High-Speed Trigger Mechanism", PA1 Swiss Patent 342,624, 15 Jan. 1960: "Electrodynamic System for the Generation of Mechanical Impulses", and PA1 the first switch is mechanically coupled to a third switch disposed on the other of the potential lines on the downstream side of the branch, in such manner as to be closed/opened at the same time as the first switch; PA1 the first switch and the second sensitive component are part of a first relay and the second switch and the first sensitive component are part of a second relay; PA1 the second relay is a monostable relay; and PA1 the first relay is a bistable relay.
British Patent 2914/58, 29 Jan. 1958: "Improvements in or relating to Electric Protective Devices".
An object of the invention is to remedy the above drawbacks and the invention is directed to a connection device adapted to connect a direct current power supply to a receiver which has a reverse polarity protection function, which is simple, light in weight and compact in size, the connection function of which is not interrupted in the event of a single failure of any of its components, in which the power dissipation is as low as possible, and which nevertheless provides efficient protection of the supply and the receiver in the event of connection of the supply with reverse polarity.